Phenylhydrazine oxalate is a specialty chemical primarily used in organic synthesis as a reagent for the preparation of various heterocyclic compounds, particularly indoles, which serve as key intermediates in the production of pharmaceuticals, dyes, and agrochemicals. It is also employed in the derivatization of carbonyl compounds, such as aldehydes and ketones, to form stable hydrazones that facilitate their identification and analysis in analytical chemistry. Additionally, it finds application in biochemical studies to investigate the structure and function of carbohydrates and other biomolecules. In the dye industry, especially textiles, it supports synthesis processes. However, it is highly toxic and requires careful handling to prevent health hazards.